bcachefs: Ensure buckets have io_time[READ] set

It's an error if a bucket is in state BCH_DATA_cached but not on the LRU
btree - i.e io_time[READ] == 0 - so, make sure it's set before adding
it.

Also, make some of the LRU code a bit clearer and more direct.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
4 files changed